A study of the Schiff base formed between pyridoxal-5′-phosphate and poly-L-lysine of low polymerization degree

Abstract

The interaction between pyridoxal-5′-phosphate (PLP) and poly-L-lysine of low polymerization degree has been studied in aqueous solutions. Formation of a Schiff base by a reversible reaction is observed according to absorption spectra and electrochemical results. The apparent equilibrium constant has been calculated as a function of the pH under conditions which favour addition of one molecule of the coenzyme to the polypeptide. A comparison of the poly-L-lysine : PLP Schiff base and Schiff bases from PLP and amino acids or amines is considered. From the study of the influence of the lysine : PLP ratio a characterization of the binding of PLP to the matrix is obtained in the pH interval 5–10. The response of the Schiff base to changes in pH or poly-L-lysine concentration point to an important role of the supporting polypeptide in the environment of the coenzyme favouring, under determined conditions, stabilization of the enolimine form or a carbinolamine intermediate.